# Full text of "Text Book Of Mechanical Engineering"

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```CHAPTER IX.

ON   ENERGY,  AND  THE  TRANSMISSION   OF  POWER
TO   MACHINES.

WE commence with a few definitions and explanations.
Force and Mass. — Engineers use * gravity' units for these:
he unit offeree being i Ib. and that of mass 32*2 Ibs. (g) or :

w

mass = —
g

Velocity is estimated in feet per second. If uniform^ the
listance travelled (s) depends both on rate and time occupied :

US)                 5 = tv   (distance — time x velocity)

shewn graphically at A, Fig. 434. The area B shews similarly the
listance travelled, under variable velocity given by the curve ; the
areas being measured as at Fig. 326, Chapter VIII.

Acceleration (/) is the increase of velocity during each
second. Uniform acceleration is produced by any constant
force, the latter being measured by the increase of momentum
it produces.* Momentum = mass x velocity.

w
. *. Force producing acceleration = — x /

o

Uniformly Accelerated Velocity. — A body starting from
rest at o {c, Fig, 434) has its velocity gradually increased by the
amount /during each second /, and the final velocity is 4/ But
the total time is 4. Therefore final velocity,

*-/' ..... (0
and the distance is shewn by the area under the velocity curve

atC>°r:          ,-iJf-i//. ..... (a)

Substituting value of t from (i) we have :

_

* Newton's second Law.```